False regarding a propagated epidemic is ?

Ans. is 'a' i.e., No secondary wave Propagated epidemics o Propagated epidemic is most often of infectious origin. o It results from person to person transmission. Source of disease agent is not common to all cases. Every new case becomes the source for others. The epidemic usually shows a gradual rise and tails off over a much longer period of time. o The speed of spread depends upon herd immunity, oppounities for contact and secondary attack rate. o Propagated epidemics are more likely to occur where large number of susceptibles are aggregated, or where there is a regular supply of new susceptible individuals (e.g. bih, immigrants) lowering herd immunity. o Transmission continues until the number of susceptibles is depleted or susceptible individuals are no longer exposed to infected persons or intermediary vectors. o Epidemic continues over more than one incubaton period. Secondary waves are seen. o Examples ---> epidemic of polio and Hepatitis A. Also know o A typical type of epidemic is epidemic of cholera. o It stas as common source epidemic ---> most of the initial cases acquire the disease from a common source (e.g. a well with contaminated water). o Then it continues as a propagated epidemic ---> these cases become the source for the other persons in their close vicinity. So it has a sharp peak but tails of gradually over a longer period of time.